Wicking and thermal characteristics of micropillared structures for use in passive heat spreaders

Abstract

The thermal and hydrodynamic performance of passive two-phase cooling devices such as heat pipes and vapor chambers is limited by the capabilities of the capillary wick structures employed.The desired characteristics of wick microstructures are high permeability, high wicking capability and large extended meniscus area that sustains thin-film evaporation. Choices of scale and porosity of wick structures lead to trade-offs between the desired characteristics. In the present work, models are developed to predict the capillary pressure, permeability and thin-film evaporation rates of various micropillared geometries. Novel wicking geometries such as conical and pyramidal pillars on a surface are proposed which provide high permeability, good thermal contact with the substrate and large thin-film evaporation rates. A comparison between three different micropillared geometriescylindrical, conical and pyramidal -is presented and compared to the performance of conventional sintered particle wicks. The employment of micropillared wick structure leads to a ten-fold enhancement in the maximum heat transport capability of the device. The present work also demonstrates a basis for reverse-engineering wick microstructures that can provide superior performance in phase-change cooling devices.

Hyperhydrophilic rough surfaces and imaginary contact angles

“…They result not only from spherical (tubes) interfaces but also from non-spherical interfaces generating forces between vertical pillars [34], spheres and/or flat walls [35]. The maximum non-dimensional capillary pressure also strongly depends on the topology of the microstructures being highest for pyramidal and lowest for cylindrical structures [36]. The filling of capillaries (imbibition) in time is governed by the well known Lucas-Washburn equation [37,38], which shows a square-root dependency of time, is proportional to the capillary radius and is maximal for h 0 = 08.…”

Design of micropillar wicks for thin-film evaporation

“…Prior thin-film evaporation studies have shown that the desired characteristics of wicks for efficient fluidic and thermal transport are small characteristic length scale, high porosity, high permeability, high capillarity, and large extended menisci [14,15].…”

The Effective Transmissivity of a Plane‐Walled Fracture With Circular Cylindrical Obstacles

“…The model can be directly used for manufactured systems such as microfluidic devices for microbiological filration or separation systems (Cady et al, 2003;Nagrath et al, 2007), high performance liquid chromatography (Song et al, 2012), dielectrophoretic platforms (Khoshmanesh et al, 2011), heat spreading, and dissipation system for microelectronic Ranjan et al (2012), which are often characterized by aperture-to-diameter ratios exceeding 1. The model can be directly used for manufactured systems such as microfluidic devices for microbiological filration or separation systems (Cady et al, 2003;Nagrath et al, 2007), high performance liquid chromatography (Song et al, 2012), dielectrophoretic platforms (Khoshmanesh et al, 2011), heat spreading, and dissipation system for microelectronic Ranjan et al (2012), which are often characterized by aperture-to-diameter ratios exceeding 1.…”

“…Although the presented model is derived for a plane-walled fracture, it could still be used to provide first-order estimates to the effective transmissivity of rough-walled fractures by introducing an equivalent aperture and treating the contact areas as obstacles. The model can be directly used for manufactured systems such as microfluidic devices for microbiological filration or separation systems (Cady et al, 2003;Nagrath et al, 2007), high performance liquid chromatography (Song et al, 2012), dielectrophoretic platforms (Khoshmanesh et al, 2011), heat spreading, and dissipation system for microelectronic Ranjan et al (2012), which are often characterized by aperture-to-diameter ratios exceeding 1.…”